The invention relates to a measuring system and method for continuous production of substantially long and flat sheet or strip of material such as copper, steel or aluminium. More particularly it is a system, a computer program product, a computer data signal, a flatness determination signal and a method for flatness measuring for use in a rolling mill.
In the rolling of strip and sheet materials it is common practice to roll a material to desired dimensions in a rolling mill stand and then feed the resulting strip to a coiler. On the coiler, the strip is wound up into a coil. Such coils are then taken off the coiler and after some time has elapsed moved on to subsequent processes such as annealing, slitting, surface treatment processes, or other processes.
The tension in the strip between a mill stand and a coiler is carefully monitored and it is known to measure tension distribution across a strip in order to regulate the flatness of the rolled material. In U.S. Pat. No. 3,481,194 Sivilotti and Carlsson disclose a strip flatness sensor. It comprises a measuring roll over which the strip passes between a mill stand and, for this example, a coiler. The measuring roll detects the pressure in a strip at several points across the width of the strip. The pressure represents a measure of the tension in the strip. The measurements of tension in the strip result in a map of flatness in each of several zones across the width of the strip. U.S. Pat. No. 4,400,957 discloses a strip or sheet mill in which tensile stress distribution is measured to characterise flatness. The measures of flatness are compared to a target flatness and a difference between measured flatness and target flatness is calculated, as a flatness error. The flatness error is fed back via a control unit to the actuators of the mill stand, so as to regulate and control flatness in the strip in order to approach a zero flatness error.
Different sensors, gauges, and/or transducers generate input values to a system for flatness measurement. Said system comprises different measurement systems or blocks for determining quantities like strip tension, distributed force, and finally flatness.
The quantity strip tension is a measured value corresponding to the force of the strip against the measuring roll. Said force is registered by means of tensiometer load cells, which are fixed at shaft bearings of the measuring roll. Strip tension is an important quantity for determining the average force on the roller and on each measuring device.
Some necessary input quantities, like the wrap angle of the strip over the measuring roll, have not been determined by means of any measuring devices. They have been pre-loaded into the system and if a value is changing during the process it has been adjusted for an example, by calculation. In U.S. Pat. No. 3,481,194 Sivilotti and Carlsson prescribe a certain angle for the passing of the strip over the measuring roll. The wrap angle is an important value when calculating other values of interest. It is used for calculating the Distributed Force per sensor on the measuring roll. The wrap angle depends on the radius of the coil on the coiler. The wrap angle will change when the radius of the coil grows and, therefore, the value of the wrap angle has to be adjusted during the process.
As shown above, prior art systems comprise different sensors for registering and measuring different quantities and, as a consequence thereof, different measurement blocks corresponding to said quantities. Said systems are quite complex and expensive. The cost for construction and support increases rapidly with growing complexity and increasing number of different systems and sensing devices like sensors and transducers.
Thus, a system for measuring flatness having less different details, but still able to generate at least the same result as a prior art system, is preferable.
It is an object of the invention to provide a flatness measuring system using measurement output signals only generated at the contact surface of a measuring roll and not elsewhere, e.g. at the shafts, for flatness determination and calculation. It is further an object of the invention to suggest a flatness measuring system comprising less number of different sensing devices and system blocks. It is another object of the invention to suggest a flatness measuring system and method wherein the wrap angle is continuously measured and determined. It is a further object of the invention to reduce the number of necessary input signals. It is a yet further object of the invention to provide a system and a method to measure the flatness of a strip. It is yet another object of the invention to provide a more correct value of the flatness.
The invention may be described as a flatness measuring and determining system and method in which flatness of a given strip is of rolled material, comprising a measuring roll, having a number of force/pressure sensors/transducers that are situated in a certain pattern on said roll, each sensors/transducer generating an measurement output signal Upi depending on the pressure of the flat sheet on to the transducer/sensor and a Wrap Angle xcex1 of the strip on the measuring roll. Said system also comprises a Flatness Determination Unit, said unit being arranged for calculating a Wrap Angle value based on said measurement output signals, and, based thereon, the flatness of the strip. The present invention also provides a computer program product, a computer data signal and a flatness determination signal for accomplishing said objects of the invention.
The main advantage of the invention is that the system contains a reduced number of different measuring blocks and different sensors/transducers.
Another advantage is that the system is not so complex and expensive. A further advantage is that the system uses a measured value of the Wrap Angle and not an estimated value and therefore the system will provide a more correct value of the flatness.